The latest webgl 20 and vertex array object might need a bit of tweaking or the generateBabylonHDR functions do.
the update cause more webgl error when using a pre processed HDR file produced using the generateBabylonHDROnDisk:
[.Offscreen-For-WebGL-0x7f9edb812e00]GL ERROR :GL_INVALID_OPERATION : glTexImage2D: invalid internalformat/format/type combination 0x8814/0x1907/0x1406
196/#UTEVJ#0:1 [.Offscreen-For-WebGL-0x7f9edb812e00]RENDER WARNING: texture bound to texture unit 0 is not renderable. It maybe non-power-of-2 and have incompatible texture filtering.
I made a Test Pre Process HDR Skybox playground to show the problem... @Sebavan and or @Deltakosh ... I am pinging you guys here 